Platelet activating factor (PAF) is a relatively recently characterized, potent lipid which is now recognized as a pivotal mediator of acute inflammatory and allergic reactions. Of interest, a PAF-like mediator is present in normal human mixed saliva; however, the structural characterization of salivary PAF and its biological relevance in oral biology remain to be determined. Thus, the long-term objective of the proposed studies is to characterize human salivary PAF with respect to identification of its structure and elucidation of factors which modulate its concentration and biological activities in saliva. Specifically, these studies will: (1) identify factors which modulate the levels of salivary PAF; (2) determine the structures and biological activities of salivary PAF; (3) identify the source of salivary PAF; (4) characterize the PAF inhibitor(s) in normal human mixed saliva; and (5) evaluate the levels of both PAF and its inhibitor in mixed saliva obtained from individuals with varying degrees of periodontal disease. The data obtained will provide new and important information to facilitate a basic understanding of how this lipid may be involved in modulating normal as well as abnormal inflammatory processes in the oral cavity.